This application relates to corroded and pitted steel surfaces and the removal and measurement of chloride ions present thereon, which ions are known to promote corrosion of steel surfaces.
Chloride ions an known to accelerate the corrosion on of steel surface (Publ. Ref. 1). Before a steel surface is painted, it is desirable to know whether chloride ions are present and their contamination level since painting over chloride ions will allow corrosion to proceed under the paint coat (Publ. Ref. 2). As little as 10 xcexcg. chloride ion per square cm. of steel surface will accelerate the corrosion of steel surfaces (Publ. Ref. 3).
Chloride ion contamination of steel surfaces is a widespread problem caused by circumstances as diverse as the ocean shipping of steel and the use of salt on road surfaces such as bridges in winter.
Drastic steps, such as sandblasting of steel surfaces, often are used to remove corrosion products and chlorides prior to painting. However, one sandblasting step often is not enough to remove all the chloride ions, and rapid corrosion after sandblasting can occur overnight under humid conditions (Publ. Ref. 4).
In addition to the prevalence of chloride contamination of steel surfaces and the difficulty of removing chloride ion contamination, it is also difficult to obtain a valid measurement of the concentration level of chloride ions present on a steel surface.
Bresle Sampler
The Swedish Fire Research Laboratory (Brandforsk) developed a means of measuring chloride contamination with a Bresle Sampler (Publ. Ref 5). The Sampler is configured to be adhered to a surface with a cavity of known dimension and volume. Distilled or deionized water is injected into the cavity by syringe needle through a rubbery film. Removal of the water after one minute contact is also accomplished with a syringe needle. The water removed is analyzed by chemical reagents for its chloride content using reagents included in the Bresle Kit. Chloride contamination after fires occurs by formation of hydrogen chloride through burning of polyvinylchloride plastics and other chlorine-containing plastics.
While the Bresle Sampler is useful for removing readily extracted chlorides from steel surfaces Boocock has shown that not all chlorides arm removed from corroded and pitted steel surfaces by water washing and includes data obtained with a Bresle Sampler (Publ. Refs 6 and 7).
Flores (Publ. Ref. 8) also studied the performance of the Bresle Sampler.
While the reason for the difficulty of completely extracting chloride ions by water washes is not known for a certainty, it is believed to be caused by a phenomenon described as xe2x80x9cElectrolytic Confinement,xe2x80x9d which will be described later.
xe2x80x9cElcometer 134xe2x80x9d
In January 1999, a new test method for chlorides became known to applicant through commercial literature issued by KTA Tator, Inc. as new instrument offerings (Publ. Ref. 9).
Literature printed by Elcometer, Inc., 1893 Rochester Industrial Drive, Rochester Hills, Mich. 48309-3342 (Publ. Ref. 10) describes the testing process a follows in the brochures on xe2x80x9cElcometer 134xe2x80x9d and the xe2x80x9cCHLOR*TEST.xe2x80x9d
1. Empty the entire contents of the CHLOR*EXTRACT(trademark) container into the CHLOR*SLEEVE(trademark). Peel off the protective backing, pinch the sleeve to expel some of the air and adhere the sleeve to the surface to be tested.
2. Massage the extract against the surface; then peel the sleeve off the surface and place it in the perforated hole in the box lid.
3. Snap the sealed ends off the glass tube, insert it into the sleeve and down into the extract. In about two minutes read the color change to identify the chloride level in both parts per million and micro grams per centimeter squared; the ratio is 1:1.
Applicant does not know of any publication which has measured the efficiency of extraction of chlorides from standard rusted panels using the xe2x80x9cElcometer 134xe2x80x9d test method.
It is clear that xe2x80x9cElcometer 134xe2x80x9d is not an electrochemical test meter, but is a chemical method using an extraction solution and a Kitagawa absorbent tube for chloride measurement.
I am aware of the following Prior Art:
Of the Patents Listed Above, the Following Patents Describe Conductivity Cells and their Use:
U.S. Pat. No. 3,497,442
U.S. Pat. No. 3,710,237
U.S. Pat. No. 3,808,523
U.S. Pat. No. 3,829,761
U.S. Pat. No. 3,849,723
U.S. Pat. No. 3,953,790
U.S. Pat. No. 4,032,296
U.S. Pat. No. 4,331,923
U.S. Pat. No. 4,362,994
U.S. Pat. No. 4,383,221
U.S. Pat. No. 4,427,945
U.S. Pat. No. 4,833,413
U.S. Pat. No. 5,194,814
U.S. Pat. No. 5,266,899
U.S. Pat. No. 5,543,717
U.S. Pat. No. 5,483,166
U.S. Pat. No. 5,612,622
None of the above patents describes a conductivity cell for measuring chloride ions on rusted steel. U.S. Pat. No. 4,331,923 employs a low amplitude AC square wave current to measure conductivity while U.S. Pat. No. 5,543,717 uses a rectangular waveform and mentions use of sine waves for conductivity measurement. Although such waveforms are generally similar to the waveforms employed with the Johnson Cell (J-Cell) of this invention to release chloride Ions and to measure conductivity, none of the above patents employs a high frequency waveform in a pre-measurement step to free chloride ions from rusted steel.
While alternating current and/or impedance have been employed to measure corrosion in the following US patents, none of these patents mentions use of high frequency alternating current of any waveform being used to free chloride ions from corroded steel surfaces, nor is the any mention of its use to wash away chloride ion contamination from steel surfaces when employed with a flowing stream of water as described in the Embodiment of our invention.
U.S. Pat. No. 4,019,133
U.S. Pat. No. 4,181,852
U.S. Pat. No. 4,238,298
U.S. Pat. No. 4,800,165
U.S. Pat. No. 4,806,849
U.S. Pat. No. 4,962,360
U.S. Pat. No. 5,221,893
U.S. Pat. No. 5,583,426
The Remaining Patents in Prior Art are Briefly Described Below:
U.S. Pat. No. 3,491,012: Describes a means of refinishing a pitted electrode assembly while maintaining equal areas in the electrodes used.
U.S. Pat. No. 3,830,480: Sampler for molten metal to measure metal temperature and its gaseous content.
U.S. Pat. No. 3,850,736: Device for catholically polarizing two duplicated electrodes with substantially no interference with corrosion current measurement with said electrodes.
U.S. Pat. No. 3,878,064: Pitting tendency is qualitatively measured by current flowing to equal the open-circuit cathode-reference electrode potential under a restricted oxygen access condition.
U.S. Pat. No. 4,101,828: A water saturated filter paper is placed on a metal surface, and the electrical resistance of the chemical solution in the filter paper is measured to indicate when the water has extracted contaminants from the metal surface that requires washing of the metal surface to remove corrosive chemicals from the metal surface. Although a square wave current is employed, there is no indication of its use to remove trapped chloride or to measure the chloride ions present except an a screening procedure to indicate a contamination level requiring washing of the metal surface to remove corrosive contamination collected on the metal surface. The square wave is used to eliminate formation of chemical cells within the sample to be measured.
U.S. Pat. No. 4,226,693: A temperature control is an integral part of a corrosion probe.
U.S. Pat. No. 4,563,427: A corrosion test assembly is described for placement in a flowing gaseous medium for subjection to corrosive materials therein, more particularly, in scrubber systems.
U.S. Pat. No. 5,286,357: A corrosion sensor is described for detecting corrosion of a surface incorporating the sensor. The sensor is a thin flexible ion-conducting film and an overwrap of at least two thin flexible metallic electrodes whose current by electrochemical action upon corrosion is measured.
U.S. Pat. No. 5,310,470: A light-weight corrosivity senor is provided comprising a thin, non-conductive base and two electrically isolated conductive dements to the surface thereof. The sensor is connected to a current measuring means for determining current across the two conductive elements as an indicator of a corrosive environment.
U.S. Pat. No. 5,437,773: Measures deposited chloride ions on surfaces with an ion specific electrode but does not extract chloride ions from rusted steel.
U.S. Pat. No. 5,674,375: This patent detects corrosion of cathodically protected steel structures in soil and concrete in which the cathodic protection circuit is subjected to an eletrochemical impedance spectroscopic analysis with corrosion indicated by the present of a Warburg impedance. No extraction or measurement of chloride or other corrosion promoting ions is mentioned.